JP7410377B2 - How to detect signs of drill damage - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act February 28, 2019 Pamphlets were distributed and the contents of the pamphlets were explained.

The present invention relates to a method for detecting signs of drill breakage, which detects signs of drill breakage when drilling with a processing machine.

When drilling holes in extremely hard tungsten carbide workpieces using a tungsten carbide drill with a diamond-coated tip, the drill is replaced after a certain number of holes have been drilled, considering safety rather than the average lifespan of the drill. Was. Since drills made of tungsten carbide are expensive, there is a demand for using them to the fullest lifespan.

Patent Document 1 discloses an abnormality detection method that detects abnormal sounds with a sensor and determines the replacement timing standard for a cutting tool. Patent Document 2 discloses an abnormality sign detection method that measures vibrations of the axis of a cutting blade in the X and Y directions.

Japanese Patent Application Publication No. 2018-111171 JP 2017-226027 Publication

In Patent Document 1, in the case of a thin drill with a diameter of about 1 mm, it is considered difficult to detect damage to the drill using a sound sensor. As in Patent Document 2, it is presumed that it is difficult to detect signs of a fracture mode involving a workpiece only by vibration of the drill.

An object of the present invention is to provide a method for detecting signs of drill breakage that can reliably detect signs of drill breakage.

A drill failure sign detection method for detecting signs of drill failure when drilling into a workpiece according to the present invention detects vibration of the workpiece, performs frequency analysis of the vibration, and detects the amplitude of a predetermined frequency component. The present invention is characterized in that a drill failure sign detection is output when the value changes by a predetermined threshold value or more from the value of a drill for which no sign was detected.

The drill failure sign detection method of the present invention detects the vibration of a workpiece, performs frequency analysis of the vibration, and detects when the amplitude of a predetermined frequency component changes by a predetermined threshold or more from the value of a drill in which no sign was detected. Outputs detection of signs of drill damage. Since signs of drill breakage are detected from the vibration of the workpiece, it can be detected even if the drill diameter is small, and signs of failure modes involving the workpiece can also be appropriately detected, so signs of drill breakage can be detected. can be detected reliably.

1(A) and 1(B) are explanatory diagrams of a system of a method for detecting signs of drill breakage according to a first embodiment of the present invention, and FIG. 1(C) is an explanatory diagram of a system according to a modified example of the first embodiment. FIG. 2 is an explanatory diagram of a system of a method for detecting signs of drill breakage. Flowchart of the method for detecting signs of drill damage according to the first embodiment Flowchart of the method for detecting signs of drill damage according to the second embodiment Flowchart of the method for detecting signs of drill damage according to the second embodiment Vibration image during the first test Vibration image during the first test Vibration image during the second test Vibration image during the second test

[First embodiment]
Hereinafter, a method for detecting signs of drill damage according to the first embodiment will be explained based on the drawings. FIG. 1(A) is an explanatory diagram of a system of a method for detecting signs of drill breakage according to the first embodiment.
The processing machine 10 is movable in the vertical direction by a spindle motor (main axis motor) 30 driven by three-phase alternating current and a Z-axis motor 40 provided on the column 12. The spindle unit 20 includes a spindle unit 20, a spindle 18 rotatably held by the spindle unit 20 and rotationally driven by a spindle motor 30, and a drill T attached to the tip of the spindle 18. The processing machine 10 is further equipped with a drill changer 50 for changing drills. As shown in FIG. 1(B), the drill T is used to drill a hole in a workpiece W that is fixed by a pair of clamps 16A and 16B to a moving table 14 that moves on the XY axis. . An acceleration sensor 52 is attached to the clamp 16B to detect vibrations in the Z direction of the machining axis. The acceleration sensor 52 is connected to a drill failure sign detection device 100.

A current sensor 32 is attached to a three-phase AC power supply 34 that drives the spindle motor 30. A current sensor 42 is attached to a three-phase AC power supply 44 that drives the Z-axis motor 40. The current sensor 32 and the current sensor 42 are connected to a drill damage sign detection device 100. The drill damage sign detection device 100 is composed of a computing device such as a computer and a microcomputer board. The drill breakage sign detection device 100 stores a program that executes the drill breakage sign detection method of the first embodiment. If the drill breakage sign detection device is comprised of a microcomputer board, the drill breakage sign detection device can also be attached to a control device such as a sequencer on the processing machine 10 side. The vibration of the workpiece W is measured by the acceleration sensor 52 and outputted to the drill failure sign detection device 100. The current sensor 32 measures the load current of the spindle motor 30 and outputs it to the drill failure sign detection device 100 side. The current sensor 42 measures the load current of the Z-axis motor 40 and outputs it to the drill failure sign detection device 100 side. The drill breakage sign detection device 100 detects drill breakage signs based on the vibration of the workpiece W, the load current of the spindle motor 30, and the load current of the Z-axis motor 40. Here, load current, which is easy to detect, is used to detect the motor load, but detection accuracy can also be improved by detecting load power.

The workpiece W is an extrusion mold for manufacturing a DPF (diesel particulate filter) made of tungsten carbide. Drill T is a 1.2 mm diameter drill made of tungsten carbide with a diamond-coated tip. The extrusion mold is first formed with a matrix-like non-through hole on one surface of the mold using a processing machine 10 shown in FIG. Then, in the next step, honeycomb-shaped slits communicating with the non-through holes for extruding the ceramic material having honeycomb-shaped openings are formed on the opposite surface of the matrix-like non-through holes.

The detection principle of the method for detecting signs of drill breakage according to the first embodiment will be explained. It was found that when the drill becomes dull, the tip becomes less likely to bite, and low-frequency vibrations are generated on the workpiece side. On the other hand, it was found that when a drill becomes fatigued, it bends and hits the workpiece sideways, producing high-frequency vibrations. It has been found that by detecting these low frequency vibrations and high frequency vibrations, it is possible to detect signs of drill damage.

Furthermore, when viewed from the motor current side, there are two modes in which a drill breaks: a Z-axis mode in which the drill breaks due to a load during machining in the Z-axis direction, and a spindle axis mode in which it breaks due to a load in the drill rotation direction. found. Z-axis mode occurs when the tip of a tungsten carbide drill is coated with diamond, and the cutting force decreases as the diamond coating becomes thinner, causing the cutting force to fall below the pushing force (Z-axis feed force). It is thought that this is not the case. The spindle shaft mode is considered to be caused by wear or metal fatigue of the entire drill and the thread being broken when screwed in while the drill is rotating. It has also been found that a sign of damage in the Z-axis mode can be detected by an increase in the load current of the Z-axis motor 40. Furthermore, it has been found that a sign of damage in the spindle axis mode can be detected by an increase in the load current of the spindle motor 30. It has been found that by using these two together, it is possible to detect signs of damage in the Z-axis mode and spindle axis mode.

In the first embodiment, signs of damage to the drill can be reliably detected by using the motor current in addition to the low-frequency vibration and high-frequency vibration on the workpiece side described above. In the first embodiment, signs of drill breakage are detected using the vibration of the workpiece and motor current, but signs of drill breakage can be detected at a practically sufficient level only by the vibration of the workpiece.

In the method for detecting signs of drill damage according to the first embodiment, the current of the motor is detected, and the average value of the effective values is calculated by shifting the time window within a predetermined time of one hole machining time with the drill. The minimum value from the average value of the effective values is used to determine whether the current has changed by a predetermined threshold value or more from the value in the drill where no sign was detected. Therefore, it is possible to eliminate the influence of noise and accurately detect signs of drill damage.

FIG. 2 is a flowchart of the method for detecting signs of drill damage according to the first embodiment.
The drill damage sign detection device 100 acquires vibration values in the Z direction of the machining axis from the acceleration sensor 52 by sampling at 2 kHz (S12), performs frequency analysis using short-time Fourier transform (S14), and obtains vibration values from 10 Hz to 200 Hz. Find the vibration value (amplitude value) for each frequency. The drill failure sign detection device 100 determines whether the vibration value has changed significantly based on whether the vibration value in the drill for which no sign was detected was greater than a predetermined threshold value in the low frequency range (for example, 10 Hz to 90 Hz). S16). As the threshold value, a value that is 1.2 to 2 times the amplitude value of the drill in which no sign was detected can be adopted. If the change in value is small (S16: No), the drill breakage sign detection device 100 detects a large change in the value depending on whether the vibration value becomes larger than the previous vibration value by a predetermined threshold or more in the high frequency range (for example, 110 Hz to 190 Hz). It is determined whether the process has been completed (S18). If there is no significant change, the process proceeds to step 22. On the other hand, if the vibration (amplitude) becomes large in the low frequency range (16: Yes) or if the vibration (amplitude) becomes large in the high frequency range (18: Yes), a sign detection notification is performed ( S30). Here, the drill damage sign detection device 100 instructs the drill changer 50 to replace the drill.

If there is no sign of drill breakage from the vibration (S18: No), the drill breakage sign detecting device 100 detects a sign of drill breakage from the motor current. First, the drill failure sign detection device 100 acquires the Z-axis current (S22), and shifts the time window by 3 seconds for a predetermined time (between 4 seconds and 12 seconds) of the one-hole machining time (38 seconds). The average value of the effective values is calculated (S24), and the minimum value is adopted from the calculated average values of the plurality of effective values (S26). The drill failure sign detection device 100 determines whether the value has changed significantly based on whether the value has become larger than the minimum value of the average value of the effective values of drills for which no sign was detected the previous time by a predetermined threshold value or more. As the threshold value, a value that is 1.2 to 2 times the minimum value of the average value of the effective values of drills in which no signs were detected can be adopted. If the change in value is small (S28: No), the process proceeds to step 32. On the other hand, if the change in the value of the Z-axis current is large (S28: Yes), a sign detection notification is performed (S30). Here, the drill damage sign detection device 100 instructs the drill changer 50 to replace the drill.

In step 32, the drill failure sign detection device 100 acquires the spindle shaft current and shifts the time window of 3 seconds by a predetermined time (between 22 seconds and 30 seconds) of the one-hole machining time (38 seconds). The average value of the values is calculated (S34), and the minimum value is adopted from the average value of the plurality of calculated effective values (S36). The drill failure sign detection device 100 determines whether the value has changed significantly based on whether the value has become larger than the minimum value of the average value of the effective values of drills for which no sign was detected the previous time by a predetermined threshold value or more. As the threshold value, a value that is 1.2 to 2 times the minimum value of the average value of the effective values of drills in which no signs were detected can be adopted. If the change in value is small (S38: No), the process proceeds to step 42 and continues until the end of machining. On the other hand, if the change in the value of the spindle shaft current is large (S38: Yes), a sign detection notification is performed (S30). Here, the drill damage sign detection device 100 instructs the drill changer 50 to replace the drill.

[Modification example of the first embodiment]
FIG. 1(C) is an explanatory diagram of a system of a method for detecting signs of drill breakage according to a modified example of the first embodiment.
The drill T is used to drill a hole in a workpiece W that is fixed to a movable table 14 that moves on the XY axis with a pair of clamps 16A and 16B. In a modification of the first embodiment, each of the pair of clamps 16A, 16B is provided with an acceleration sensor 52A, 52B, and outputs are sent from the two acceleration sensors 52A, 52B to a drill failure sign detection device. The drill breakage sign detection device according to the modified example of the first embodiment performs sign detection by summing the outputs from the two acceleration sensors 52A and 52B. Therefore, even if the drill T processes a position away from one sensor, the machining position approaches the other sensor, so the predictive accuracy is not affected by the machining position.

[Second embodiment]
The mechanical configuration of the drill failure sign detection device 100 of the second embodiment is the same as that of the first embodiment shown in FIG. 1(A).
FIG. 3 is a flowchart of a drill failure sign detection method according to the second embodiment.
The drill failure sign detection device 100 acquires the vibration value in the machining axis Z direction from the acceleration sensor 52 by sampling at 2 KHz (S12), performs frequency analysis using short-time Fourier transform (S14), and performs a frequency analysis using short-time Fourier transform. An image of vibration values for each frequency of 10 Hz to 200 Hz as shown in FIG. 8 is formed (S46). Then, compare the vibration value waveform in the image from the previous processing with the vibration value waveform in the current image, quantify the difference, and compare it with the difference value between the vibration value waveform from the time before last and the previous vibration value waveform. , 1.2 to 3 times or more, it is determined whether the image pattern has changed significantly (S48). If the image pattern has not changed significantly (S48: No), the process moves to step 42. If the image pattern has changed significantly (S48: Yes), a sign detection notification is performed (S30). Here, the drill damage sign detection device 100 instructs the drill changer 50 to replace the drill.

FIG. 4 is a flowchart of signal correction from the acceleration sensor in the method for detecting signs of drill breakage according to the second embodiment.
The drill damage sign detection device 100 acquires the machining position of the drill (S52), calculates the distance from the acceleration sensor 52 to the machining position (S54), and calculates a correction value for correcting the amount of vibration attenuation according to the distance. Then, the signal is corrected from the acceleration sensor (S58). In the drill breakage sign detection method of the second embodiment, the sign accuracy is not affected by the machining position.

The test results for workpiece vibration and drill damage will be explained with reference to the frequency analysis images of FIGS. 5 to 8.
FIGS. 5 and 6 show frequency analysis images of around 351 holes in which drill damage occurred during the first test. Here, sampling is performed at 2 KHz, the vertical axis represents the frequency from 10 Hz to 200, the horizontal axis represents the machining time for forming one hole, and the change in color represents the magnitude of vibration.

The image of the 351st hole is B-6 in FIG. The image of 350 holes is B-5, the image of 349 holes is B-4, the image of 348 holes is B-3 in Figure 5, the image of 347 holes is B-2, and the image of 346 holes is B-1. . The image of the 345th eye hole is A-6 in FIG. The image of the 344th hole is A-5, the image of the 343rd hole is A-4, the image of the 342nd hole is A-3 in Figure 5, the image of the 341st hole is A-2, and the image of the 340th hole is A-1. . The image of the 352nd hole is C-1 in FIG. The image of hole 353 is C-2, the image of hole 354 is C-3, the image of hole 355 is C-4 in Figure 6, the image of hole 356 is C-5, and the image of hole 357 is C-6. .

It can be seen that in the 350th hole (B-5), which is one hole before the 351st hole (B-6) where drill damage occurred, the vibration is especially large at 100 Hz or less.

FIGS. 7 and 8 show frequency analysis images around 811 holes in which drill damage occurred during the second test.

The image of the 811th hole is E-4 in FIG. The image of hole 810 is E-3 in FIG. 7, the image of hole 809 is E-2, and the image of hole 808 is E-1. The image of the 307th eye hole is D-6 in FIG. The image of hole 806 is D-5, the image of hole 805 is D-4, the image of hole 804 is D-3 in Figure 7, the image of hole 803 is D-2, and the image of hole 802 is D-1. . The image of the 812th hole is E-5 in FIG. 8, the image of the 813rd hole is E-6, and the image of the 814th hole is F-1 in FIG. The image of hole 815 is F-2, the image of hole 816 is F-3, the image of hole 817 is F-4 in Figure 8, the image of hole 818 is F-5, and the image of hole 819 is F-6. .

In the 808 hole (E-1), the 808 hole (E-1), the 809 hole (E-2), and the 810 hole (E-3), which is the third hole before the hole number 811 (E-4) where drill damage occurred, It can be seen that the vibration (amplitude) is large below 30 Hz and between 100 Hz and 190 Hz.

From the test results described above, it has been found that a sign of drill damage can be detected by detecting low-frequency vibrations and high-frequency vibrations of the workpiece or from changes in the image pattern.

10: Processing machine 14: Moving table 16: Clamp 30: Spindle motor 32: Current sensor 40: Z-axis motor 42: Current sensor 50: Drill changer 100: Sign detection device T: Drill W: Workpiece

Claims (3)

A method for detecting signs of drill damage when drilling into a workpiece, in which vibrations of the workpiece are detected by an acceleration sensor attached to a clamp that fixes the workpiece, and Frequency analysis of the vibration of the object is performed to determine whether the amplitude of the low frequency range of 10 to 90 Hz has changed by more than a predetermined threshold value from the value of the drill where no sign was detected, and the amplitude of the low frequency range is determined to be the level at which the sign is detected. If the value has not changed by more than a predetermined threshold from the value for the drill where no sign was detected, it is further determined whether the amplitude of the high frequency range from 110 to 190 Hz has changed by more than a predetermined threshold from the value for the drill for which no sign was detected. , when the amplitude of the low frequency range changes by more than a predetermined threshold from the value of a drill where no sign was detected , or when the amplitude of the high frequency range changes by more than a predetermined threshold from the value of a drill where no sign was detected. A method for detecting a sign of drill breakage, the method comprising: outputting a sign of drill breakage when the drill breaks. The method for detecting signs of drill breakage according to claim 1 , comprising:
Furthermore, detecting at least one of the current of the main shaft motor that drives the drill and the current of the Z-axis motor that sends the drill to the workpiece side,
When at least one of the current of the main shaft motor and the current of the Z-axis motor changes by a predetermined threshold value or more from a value in a drill in which no signs were detected, a drill failure sign detection is output. Premonition detection method. The sign detection method according to claim 1 or claim 2 ,
A method for detecting signs of drill breakage, characterized in that the vibration of the workpiece is detected by the acceleration sensor along a machining axis of the drill.

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